Solenoid valve for controlling a fuel injector

ABSTRACT

A solenoid valve valve part for controlling a fuel injector in a fuel injection system has a valve needle, the open and closed positions of which may be controlled by the solenoid valve valve part. The solenoid valve valve part has a valve ball which rests on a valve seat and which lifts up from the valve seat when current flows through the solenoid valve valve part. The valve seat is in hydraulic connection with the fuel injector via a borehole. When the valve ball lifts up from the valve seat, a pressure medium such as high-pressure fuel flows through the borehole into a pressure relief chamber in the solenoid valve valve part. In the further progression this causes the fuel injector to open. To prevent the formation of cavitation bubbles and the damage thus caused, the borehole includes, at least in part, one or more sections having a cross section which continuously expands in the direction of the valve seat. A separation in flow brought about by sharp transition edges, which may cause cavitation bubbles, is thus counteracted.

FIELD OF THE INVENTION

[0001] The present invention relates to a solenoid valve for controllinga fuel injector.

BACKGROUND INFORMATION

[0002] Solenoid valves are used to control fuel injectors in a fuelinjection system having a valve needle, the open and closed positions ofwhich may be controlled by the solenoid valve.

[0003] The solenoid valve has a valve ball, which lifts up and opens avalve seat when current flows through the magnet assembly of thesolenoid valve. This valve seat is in hydraulic connection with thecontrol pressure chamber of the fuel injector via a borehole. When thevalve seat opens, the pressure in the pressure chamber of the fuelinjector drops, and the fluid (pressure medium) flows through theborehole in the direction of the valve seat and further into a pressurerelief chamber. This causes the valve needle or the fuel injector toopen.

[0004] It is believed that the common rail injector (CRI) operatesaccording to this conventional operating principle, which permits a maininjection and a pilot injection having very brief injection times. Sucha solenoid valve is referred to, for example, in German Published PatentApplication No. 196 50 865.

[0005] Cavitation may cause severe damage to the valve seat of the valvepart. The borehole extending through the valve part includes acylindrical A-throttle adjoining a pilot borehole in the controlpressure chamber of the fuel injector, and a subsequent cylindricaldiffuser bore leading to the valve seat. The cavitation damage may, forexample, occur in the region of an abrupt transition from the diffuserbore to the valve seat. This damage may cause “washout” of the seatedge. As the damage increases, this edge may break off, resulting intotal failure of the injector and operational failure of the vehicle. Tosolve this problem, the formation of cavitation bubbles should bereduced, and the site of implosion of any remaining bubbles should beshifted to a location, such that this effect no longer influences thecorrect functioning of the injector.

SUMMARY

[0006] An exemplary solenoid valve according to the present inventionincludes a borehole which has, at least in part, one or more sectionshaving a cross section that continuously expands in the direction of thevalve seat. Sharp-edged transitions within the borehole, for example, inthe transition region from the A-throttle to the diffuser bore, may thusbe avoided. It is believed that a conical geometry of the expandingsection is advantageous.

[0007] A severe separation in flow may occur when the fluid (pressuremedium) flows through the A-throttle to the outlet edge downstream,which is sharp-edged due to the manufacturing process, toward thediffuser bore. Dead water and recirculation areas may form at thoselocations. These effects may result in fluctuations in thereproducibility of the amount of fluid flowing through, as well as inthe formation of zones at partial vacuum and cavitation bubbles.

[0008] Further within the borehole, the flow again contacts the borewalls. Shortly before reaching the throttle point at the valve seatsituated further downstream, the pressure in the medium rises again andthe cavitation bubbles floating in the liquid stream implode, therebycausing the described cavitation damage at the wall of the flow channel.

[0009] As a result of the borehole of an exemplary solenoid valveaccording to the present invention, the flow geometry in the valve partis altered, so that a generally turbulence-free transition of the mediumfrom the A-throttle to the valve seat may be achieved without thedescribed negative effects.

[0010] The transition from the A-throttle to the diffuser bore may, forexample, be formed with a continuously expanding cross section, so thatthe borehole includes three sections that merge into one another. Inthis manner, separation of the flow at the sharp-edged outlet edge maybe prevented.

[0011] Furthermore, the borehole, for example, may be divided into threesections: the A-throttle, the diffuser bore adjoining the sectionexpanding in cross section, and the diffuser bore, the A-throttle andthe diffuser bore having substantially the same length. It is believedthat, in conventional designs, the A-throttle directly adjoins thediffuser bore, the latter having a greater length than the former. In anexemplary embodiment according to the present invention, both theA-throttle and the diffuser bore may be considerably shortened, therebylowering the pressure, for example, in the diffuser bore. In conjunctionwith the continuously expanding (e.g., conical) transition regionbetween the A-throttle and the diffuser bore, an optimum shape of theflow channel may be obtained, in which no cavitation bubbles are formed,and no implosions of these bubbles are observed.

[0012] In another exemplary embodiment according to the presentinvention, the borehole upstream from the valve seat has multiple, forexample, conical, sections expanding in the direction of the valve seat.A good flow pattern may be obtained when each of the two cylindricalboreholes, e.g., the A-throttle and the diffuser bore, has a conicallyshaped section. For example, the length of the (cylindrical) diffuserbore may be reduced, so that the pressure rise within the diffuser boreis no longer sufficient to allow the implosion of any cavitation bubblesthat may form. As described above, the conical sections connecting thecylindrical boreholes prevent separation of flow and, thus, prevent thecause of cavitation bubble formation.

[0013] The aperture angles of the successive conical sections in thedirection of the valve seat may, for example, increase, thus permittinga gradual transition to the aperture angle of the valve seat. This maycreate an favorable flow pattern.

[0014] The sections that continuously expand in cross section, forexample, may be created in a simple mechanical fashion by rounding offthe respective transitions between the boreholes, such as the A-throttleand the diffuser bore. In this manner, the sharp edge of a transitionmay be machined during manufacturing to provide an optimum flow channel.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a sectional view through the valve part of a solenoidvalve.

[0016]FIG. 2 is a sectional view through the valve part of an exemplarysolenoid valve according to the present invention.

[0017]FIG. 3 is a sectional view through the valve part of anotherexemplary solenoid valve according to the present invention.

DETAILED DESCRIPTION

[0018]FIG. 1 illustrates the valve part 1 of a solenoid valve forcontrolling a conventional fuel injector. Borehole 2 leads to thecontrol pressure chamber of a fuel injector, and is in hydraulicconnection with valve seat 4 of pressure relief chamber 3 in thesolenoid valve via an additional throttle bore. The throttle bore isformed from A-throttle 6 and subsequent diffuser bore 5, an abruptchange in cross section occurring between the cylindrical boreholes atthe transition point.

[0019] When current flows through the solenoid valve, a valve ball (notshown) in pressure relief chamber 3 lifts up from valve seat 4, therebyallowing the pressure in the valve chamber to decrease in the directionof the valve ball due to the fact that a pressure medium, for example,high-pressure fuel, flows from borehole 2 via the throttle bore intopressure relief chamber 3. The pressure drop thus created in borehole 2upstream from the adjoining control pressure chamber causes the valveneedle of the fuel injector to open, and high-pressure fuel is injected.

[0020] As shown in FIG. 1, the structure formed by A-throttle 6 anddiffuser bore 5 is referred to as the throttle bore. When fluid (e.g.,pressure medium, for example, high-pressure fuel) flows through thethrottle bore, a separation in the flow occurs at the sharp edge of thetransition from A-throttle 6 to diffuser bore 5. This results inturbulence and the formation of dead water and recirculation areas. Theshearing of flow causes cavitation bubbles to form, which are highlycompressed in areas of high pressure, resulting in the risk ofimplosion. Imploding cavitation bubbles in the vicinity of the valveseat may cause damage, which, in the further progression, may result in“washout” of valve seat 4, so that proper opening and closing of thesolenoid valve, and thus of the injector, may no longer guaranteed.

[0021]FIG. 2 shows an exemplary solenoid valve according to the presentinvention in the region of valve seat 4. Identical parts from FIG. 1 areprovided with the same reference numbers in FIG. 2. A section 7 isprovided, which has a continuously expanding cross section in thethrottle bore between borehole 2 leading to the control pressure chamberand pressure relief chamber 3. In this exemplary embodiment, section 7is produced by a method that rounds off the borehole transition betweenA-throttle 6 and diffuser bore 5. Simultaneously, both A-throttle 6 anddiffuser bore 5 are considerably shortened in comparison to theconventional design shown in FIG. 1. In this manner, the flow geometrymay be improved, so that cavitation damage may be avoided to thegreatest extent possible. Thus, an exemplary solenoid valve according tothe present invention may have fail-safe operability.

[0022]FIG. 3 shows another exemplary solenoid valve according to thepresent invention in the region of valve seat 4. In this design,A-throttle 6 again adjoins borehole 2, which leads to the controlpressure chamber of the fuel injector, as a cylindrical borehole with aconsiderably reduced cross section. According to this exemplaryembodiment, a first conical section 9 follows at an aperture angle a andis followed by a cylindrical diffuser bore 10, which is considerablyshortened in comparison to earlier embodiments (see FIG. 1). Diffuserbore 10 is followed by a section 11 having a conically expanding crosssection that opens into valve seat 4. Conical section 11 has an apertureangle β.

[0023] In this exemplary embodiment according to the present invention,aperture angle a is 50°, and angle β is 60°. Overall, the aperture angleof the flow channel is thus successively expanded to merge into thevalve seat. The flow pattern may be very favorably influenced by thismeasure. The combination using the greatly shortened diffuser bore 10prevents excessive pressure rises, which may allow any cavitationbubbles present to implode. The complete profile of the flow channel ofborehole 8 is illustrated in FIG. 3, and is denoted by reference number12.

[0024] The present invention may be used in any given cross section of aborehole, and the solenoid valve according to the present invention mayinclude more than two sections having expanding cross sections withinborehole 8. It is believed that the exemplary solenoid valve illustratedin FIG. 3 may sufficiently prevent cavitation damage, thus increasingthe functional reliability of common rail injectors.

What is claimed is:
 1. A solenoid valve for controlling a fuel injectorin a fuel injector system, comprising: a valve seat of a pressure reliefchamber; and a valve ball arranged on the valve seat; wherein a boreholehydraulically connects the valve seat to a control pressure chamber ofthe fuel injector, the borehole including at least one section having across section that continuously expands in a direction of the valveseat.
 2. The solenoid valve according to claim 1, wherein the boreholeincludes a first section, a second section, and a middle section merginginto one another, a cross section of the middle section continuouslyexpanding.
 3. The solenoid valve according to claim 2, wherein the firstand second sections adjoin the middle section and have lengths that aresubstantially the same.
 4. The solenoid valve according to claim 1,wherein the borehole includes two sections having respective crosssections that continuously expand, and the two sections respectivelyadjoin another section having a constant diameter.
 5. The solenoid valveaccording to claim 1, wherein the at least one section has a conicalshape.
 6. The solenoid valve according to claim 1, wherein apertureangles of successive sections of the borehole increase in the directionof the valve seat.
 7. The solenoid valve according to claim 1, whereinthe at least one section is manufactured by rounding off two boreholetransitions.